The present invention relates to a cathode-ray tube used in televisions and computer monitors, particularly to a cathode-ray tube having a particular face panel.
In cathode-ray tubes including a face panel having an approximately flat outer surface, which have been spread recently, even if deflecting distortion of electron beams is completely extinguished, the periphery of the picture appears to be embossed due to the refraction of light at the face panel. That is, a phenomenon in which the picture appears to be concave is easily generated. Because this concave impression appears more conspicuously with the increase in the thickness of the face panel, it is preferable that the face panel has a smaller thickness so as to restrain this concave impression, as well as not to increase the weight of the cathode-ray tube. On the other hand, to ensure the compressive strength of the cathode-ray tube, which is a vacuum, because a face panel close to a flat surface is less advantageous than a curved face panel, it is better to make the thickness of the face panel larger if possible.
In order to solve such contradicting problems, for example, JP-A-10-64451 discloses a cathode-ray tube including a face panel in which the thickness of the periphery of the face panel in the horizontal direction is from 20 to 30% larger than that of the center of the face panel, so that the inner surface of the face panel becomes convex to the outer surface.
However, in the above-mentioned conventional cathode-ray tube, because the thickness of the periphery of the face panel is increased by 20 to 30% only in the horizontal direction, a natural flatness impression cannot be obtained due to the distortion of the picture, etc., and also it has not been able to deal with various sizes of the screen.
It is an object of the present invention to provide a cathode-ray tube that can obtain a natural flatness impression with different sizes.
In order to solve the above-mentioned problems, it is preferable that a first cathode-ray tube of the present invention includes an envelope comprising a face panel having an approximately rectangular face portion, an approximately rectangular phosphor screen being formed on an inner surface of the face portion, and a funnel at the rear of the face panel, wherein an outer surface of the face portion is substantially flat, the inner surface of the face portion is a curved surface convex to the outer surface, and when the axis extending approximately in parallel to a long side of the phosphor screen through the center of the inner surface is X-axis, the axis extending approximately in parallel to a short side of the phosphor screen through the center of the inner surface is Y-axis, the radius of curvature of the inner surface along the X-axis is Rx, the radius of curvature of the inner surface along the Y-axis is Ry, the radius of curvature of the inner surface along a long side of the phosphor screen is Rt, the length of a long side of the phosphor screen is H, and the length of a short side of the phosphor screen is V, the following inequalities are satisfied:
1.2 H1.3923  less than Rx less than 3.00 H1.4284,xe2x80x83xe2x80x83(1)
1.2 H1.3923  less than Rt less than 3.00 H1.4284,xe2x80x83xe2x80x83(2)
and
3.0 V1.4670  less than Ry less than 6.67 V1.5453,xe2x80x83xe2x80x83(3)
and wherein the inner surface has no inflection point.
Accordingly, the picture of the cathode-ray tube can be watched with a flatness impression including a concave impression at a degree with no sense of incongruity.
Furthermore, in the first cathode-ray tube of the present invention, it is preferable that when the radius of curvature of the inner surface along a short side of the phosphor screen is Rs, the following inequality is satisfied:
3.0 V1.4670 Rs less than 6.67 V1.5453.xe2x80x83xe2x80x83(4)
Furthermore, it is preferable that a second cathode-ray tube of the present invention includes an envelope comprising a face panel having an approximately rectangular face portion, an approximately rectangular phosphor screen being formed on an inner surface of the face portion, and a funnel at the rear of the face panel, wherein an outer surface of the face portion is substantially flat, the inner surface of the face portion is a curved surface convex to the outer surface, and when the axis extending approximately in parallel to a long side of the phosphor screen through the center of the inner surface is X-axis, the axis extending approximately in parallel to a short side of the phosphor screen through the center of the inner surface is Y-axis, the radius of curvature of the inner surface along the X-axis is Rx, the radius of curvature of the inner surface along the Y-axis is Ry, the radius of curvature of the inner surface along a long side of the phosphor screen is Rt, the length of a long side of the phosphor screen is H, and the length of a short side of the phosphor screen is V, the following inequalities are satisfied:
1.2 H1.3923  less than Rx less than 1.97 H1.4231,xe2x80x83xe2x80x83(5)
1.2 H1.3923  less than Rt less than 1.97 H1.4231,xe2x80x83xe2x80x83(6)
and
3.0 V1.4670  less than Ry less than 7.44 V1.4566,xe2x80x83xe2x80x83(7)
and wherein the inner surface has no inflection point.
Accordingly, the picture of the cathode-ray tube can be watched with a natural flatness impression including no concave impression.
Furthermore, in the second cathode-ray tube of the present invention, it is preferable that when the radius curvature of the inner surface along a short side of the phosphor screen is Rs, the following inequality is satisfied:
3.0 V1.4670  less than Rs less than 7.44 V1.4566.xe2x80x83xe2x80x83(8)
Furthermore, in the first and second cathode-ray tubes of the present invention, it is preferable that Rx≈Rt or Ry≈Rs is satisfied.
Accordingly, the inner surface of the face portion can be of a simple structure.